Monoshock Swingarm Advice Needed

Higgy

Higgy

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Hi everyone.

I'm drawing up some ideas for making a monoshock swing-arm that follows the same lines as a hardtail. Ideally, my design would include the shock attaching to the same spot on the frame that the upper tubes of a hardtail would be welded.

My question is this - Does anyone offer a shock specifically designed for this, or should I just look for a shock that has the correct length and load rating? As far as a load rating, where should I begin?
 
Thanks, man. Looks like some trial and error will have to be employed. Do you think I'd be safe with a reservoir shock? Maybe one that has a whole mess of adjustment range?
 
solo2racr said:
I have found it easier to just sit down with some paper and do the math. For a simple '70's style Yamaha monoshock, you'll need the distance from the swingarm pivot to the axle and to from the swingarm pivot to the shock mount. You will also need to know where the shock is going to mount on the frame so that you can measure the angle of it compared to the swingarm pivot to shock mount "lever". The difference in lengths (swingarm pivot to axle/shock mount) and the shock angle will determine the spring rate. From there, find a OEM shock and spring that fit your needs for in/lbs in the spring and the damper eye to eye length.

To get a idea of the weight to start the math with, weigh the rear of the bike. I like to use a simple bathroom scales. Also put something under the front tire as well so the bike is off the ground the same amount front and rear. I would also use about 75% of you body weight and add that to what you weight the bike at.

Figuring out what you need is the easy part. Looking up OEM specs to find what to use is the PITA.

If ya get me the numbers, I can do the math for ya. It's easier to do it than explain it.
Click to expand...

This is cool. Thank you so much for the advice, and I will definitely take you up on the math part. I'm probably not going to get this project rolling for another 8-10 weeks, because that's how long I'll be in this doggone cast. :banghead:
 
Hi Higgy,
while you are still in the planning stage, watch the unsprung weight!
A "flying triangle" style swingarm tends to build heavy, eh?
 
fredintoon said:
Hi Higgy,
while you are still in the planning stage, watch the unsprung weight!
A "flying triangle" style swingarm tends to build heavy, eh?
Click to expand...

E'er the Voice of Reason, Fred! :thumbsup:

Heavier? Perhaps, but not by much. The seat tubes will be gone, and replaced by the upper triangle tubes, and I'll have one shock - not two.

I have two XS400s in the shed. My plan is to build one of those with the monoshock to see if I like it before I waste the XS650 frame.
 
Hi Higgy,
um, yeah, but it's a BIG shock, eh?
And although there's gotta be some kinda structure to mount the seat on, that's not relevant because whatever it is, it ain't unsprung.
I've seen photos of monoshock conversions on this site that added a second loop to the stock swingarm, musta eff nigh doubled the unsprung weight.
Just sayin', be careful the triangulated structure don't get too heavy, is all.
 

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